CN102761274B - The threshold values of former limit feedback AC-DC Switching Power Supply trembles control system and method frequently - Google Patents
The threshold values of former limit feedback AC-DC Switching Power Supply trembles control system and method frequently Download PDFInfo
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Abstract
The threshold values that the invention discloses a kind of former limit feedback AC-DC Switching Power Supply trembles control system and method frequently, threshold values trembles frequency control system by arranging a current limit threshold dither unit be connected with Cycle by Cycle flow-restriction, Cycle by Cycle flow-restriction arranges resistance and comparator, current limit threshold dither unit arranges oscillator, frequency divider and some groups of current sources and switch, current limit threshold dither unit can produce the current signal of one-period to regulate constant current frequency control unit, make system works when constant current mode, its operating frequency is shaken in certain scope periodically, to disperse electromagnetic interference EMI energy, thus significantly reduce EMI, and, threshold values is made to tremble the constant-current characteristics of control system frequently not by the impact of frequency jitter, described threshold values trembles frequently control method and described threshold values, and to tremble frequency control system corresponding.
Description
Technical field
The present invention relates to switch power technology field, in particular the threshold values of a kind of former limit feedback AC-DC Switching Power Supply trembles control system frequently.
Background technology
AC-DC control technology of former limit feedback system is the new A C-DC control technology grown up between nearest 10 years, compared with traditional secondary side feedback Switching Power Supply mechanism structure, its maximum advantage is to eliminate isolating chip and the constituent element device with isolating chip cooperating, which offers a saving the space on circuit board, reduce cost and improve the reliability of system.Former limit feedback DC power is in the larger application of the cost pressures such as charger for mobile phone, and the application very high to volume requirement such as LED drive power has the larger market share.
Fig. 1 illustrates a kind of former limit feedback AC-DC power supply control chip of prior art and the structured flowchart of application thereof, as shown in Figure 1, described former limit feedback AC-DC driving power comprises control chip, transformer, NMOS tube, described transformer comprises former limit winding Np, auxiliary winding Na and secondary winding Ns, described control chip comprise secondary ON time detecting unit, constant current frequency control unit, constant pressure control unit, with gate logic, rest-set flip-flop, PFM unit, driver element, Cycle by Cycle flow-restriction and built-in power module.
The former limit formed adopting this control chip is fed back in AC-DC power supply, and resistance R1 and resistance R2 forms sample circuit, and described FB pin is that auxiliary winding Na Voltage Feedback introduces pin, and obtains signal from resistance R1 and resistance R2 formation sample circuit.Inner at control chip, FB pin is connected to the input of output voltage detecting unit and secondary ON time detecting unit, the output of described ON time detecting unit is connected to constant current frequency control unit, the output of described output voltage detecting unit is connected to constant voltage frequency control unit, described CS pin is that former limit winding Np current detection signal introduces pin, obtains signal from NMOS tube source resistance R3.Inner at control chip, CS pin is connected to the input of Cycle by Cycle flow-restriction, constant current frequency control unit and the output signal of constant voltage frequency control unit are connected and two of door inputs respectively, the S being connected respectively to rest-set flip-flop with the output (i.e. start signal) of gate logic and the output (i.e. cut-off signals) of Cycle by Cycle flow-restriction holds and R holds, the output of described rest-set flip-flop and Q end are connected to the input of PFM unit, PFM unit is connected to driver element, the output of described driver element is connected with the OUT pin of control chip, OUT pin exports the grid being connected to NMOS tube, for driving outside power NMOS tube.VCC pin is the power pins of control chip, for being whole control chip access external power source; FB pin is simultaneously as constant current frequency control signal and constant voltage frequency control signal, its constant current FREQUENCY CONTROL is for detecting the ON time of auxiliary winding Na, so that constant current frequency control unit regulates the work period in proportion, make secondary winding Ns outputting current steadily in the value of setting, namely realize the constant current function of LED drive power; The voltage of winding is assisted when its constant voltage frequency controls for detecting secondary conducting, indirect reflection exports the voltage of winding, and then indirectly reflect the size of output voltage, and carry out by-pass cock frequency according to detected voltage swing, make output voltage stabilization in set point.CS is former limit winding Np current sense pin, for detecting peak current during former limit winding Np conducting, to realize the Cycle by Cycle current limliting in each periodic process, and then makes the energy of each periodic transfer all identical; GND is the grounding pin of chip.When the systems are operating normally, relatively auxiliary winding Na is contrary with secondary winding Ns Same Name of Ends for the polarity due to transformer primary side winding Np, and therefore when former limit winding Np conducting, FB pin is negative voltage, when being in secondary winding Ns conducting phase, because auxiliary winding Na is identical with secondary winding Ns Same Name of Ends polarity, therefore FB voltage is positive voltage, now transformer secondary winding voltage is Vs=Vo+Vz, auxiliary winding voltage Va=Vs × (NA/NS)=VFB × R2/ (R1+R2), therefore Vo=VFB × R2 × NS/ [(R1+R2) * NA]-Vz, namely output voltage is the function of feedback voltage V FB, chip regulates VFB to arrive set point by constant voltage frequency control unit, output voltage Vo can be made to be stabilized in set point, now system works is at constant voltage mode, when system works is at constant current mode, secondary ON time detecting unit determines the ON time Tons of secondary winding Ns by the time that detecting FB pin is positive voltage, and the work period T=K × Tons of certainty annuity on this basis, wherein K is proportionality coefficient.Because system works is in discontinuous mode, the energy that each cycle all will make former limit winding Np store all discharges at secondary winding Ns, average output current Iout=Ips × Tons/T=Ipp × (NS/NP) × (1/K) of such secondary winding Ns, peak current when Ips is secondary winding Ns conducting, peak current when Ipp is former limit winding Np conducting, Ns is the number of turns of secondary winding Ns, and Np is the number of turns of former limit winding Np.As long as set Ipp and K and transformer parameter like this, so the output current of secondary winding Ns is exactly a steady state value.
When system works is at constant current mode, when input voltage and output voltage are all fixed, to identical system parameters, secondary ON time Tons=(Ips × Ls)/(Vout+Vz)=Ipp × (NS/NP) × Ls/(Vout+Vz)=(Vcs/R3) × (NS/NP) × Ls/(Vout+Vz), because Vcs is the current limit threshold of chip internal, it is a definite value, all the other parameters are also definite value, therefore secondary ON time Tons is definite value, such cycle T=K × Tons is fixed value, namely when system works is at constant current mode, its operating frequency is fixing, the energy of such EMI all concentrates on this operating frequency and N subharmonic thereof, thus make EMI very large, be difficult to reach charger and LED drive system to the requirement of EMI.
Therefore, prior art existing defects, needs to improve.
Summary of the invention
Technical problem to be solved by this invention is: the threshold values of the former limit feedback AC-DC Switching Power Supply providing a kind of electromagnetic interference less trembles control system frequently.
Technical scheme of the present invention is as follows: the threshold values of a kind of former limit feedback AC-DC Switching Power Supply trembles control system frequently, comprise control chip, transformer, NMOS tube, described control chip comprise secondary ON time detecting unit, constant current frequency control unit, output voltage detecting unit, constant voltage frequency control unit, built-in power subsystem, with gate logic, rest-set flip-flop, PFM unit, driver element and Cycle by Cycle flow-restriction, described control chip also comprises a current limit threshold dither unit, and described current limit threshold dither unit is connected with described Cycle by Cycle flow-restriction; Described current limit threshold dither unit arranges oscillator, frequency divider and some groups of current sources and switch, for generation of the current signal of one-period fluctuation, and exports described Cycle by Cycle flow-restriction to; Described Cycle by Cycle flow-restriction arranges resistance and comparator; One end of described resistance is detected pin with the former limit winding current of described transformer and is connected, and the other end connects the in-phase input end of described comparator, and connects with the described output being connected current limit threshold dither unit simultaneously; The inverting input of described comparator connects internal reference voltage, and the output of described comparator is connected with described rest-set flip-flop.
Be applied to technique scheme, the threshold values of a kind of former limit feedback AC-DC Switching Power Supply trembles control method frequently, comprises the steps; A: a current limit threshold dither unit be connected with Cycle by Cycle flow-restriction is set; B: the current signal being produced one-period change by described current limit threshold dither unit; C: the resistance that described current signal is arranged through described Cycle by Cycle flow-restriction, produces a periodically variable voltage signal; D: described periodically variable voltage signal is superimposed on the current sense signal of former limit winding current detecting pin, the cyclic variation operating frequency of formation.
Adopt such scheme, in the present invention, threshold values trembles frequency control system by putting a current limit threshold dither unit, this unit can produce the current signal of one-period, for regulating constant current frequency control unit, thus make system works when constant current mode, its operating frequency, in the shake of certain scope periodically, to disperse electromagnetic interference EMI energy, thus significantly reduces EMI.In addition, shake due to frequency is periodic, and shake in the segment limit that average frequency is narrower up and down, therefore the average operating frequency of system remains fixing, thus the average output current of the system of guarantee is constant, namely threshold values trembles the constant-current characteristics of control system frequently not by the impact of frequency jitter; Further, described threshold values is trembled frequently control method and threshold values to tremble frequency control system corresponding.
Accompanying drawing explanation
Fig. 1 is limit, prior art Central Plains feedback AC-DC power control system structural representation.
Fig. 2 is the application circuit schematic diagram that in the present invention, threshold values trembles control system frequently.
Fig. 3 is the internal circuit schematic diagram of Cycle by Cycle flow-restriction in the present invention.
Fig. 4 is the internal circuit schematic diagram of current limit threshold dither unit in the present invention.
Fig. 5 be in the present invention threshold values tremble that frequently control system works in constant current mode tremble principle schematic frequently.
Embodiment
Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.
Embodiment 1
As shown in Figure 2, the threshold values present embodiments providing a kind of former limit feedback AC-DC Switching Power Supply trembles control system frequently, threshold values trembles frequency control system by arranging a current limit threshold dither unit, this unit can produce the current signal of one-period, for regulating constant current frequency control unit, thus make system works when constant current mode, its operating frequency is shaken in certain scope periodically, to disperse electromagnetic interference EMI energy, thus significantly reduce EMI.In addition, shake due to frequency is periodic, and shake in the segment limit that average frequency is narrower up and down, therefore the average operating frequency of system remains fixing, thus the average output current of the system of guarantee is constant, namely threshold values trembles the constant-current characteristics of control system frequently not by the impact of frequency jitter.
Wherein, tremble frequently control system and comprise control chip 1, transformer 3, NMOS tube 2, described control chip 1 comprise secondary ON time detecting unit 101, constant current frequency control unit 102, output voltage detecting unit 103, constant voltage frequency control unit 105, built-in power subsystem 104, with gate logic 106, rest-set flip-flop 107, PFM unit 108, driver element 109, Cycle by Cycle flow-restriction 110 and a current limit threshold dither unit 111.
Wherein, described current limit threshold dither unit 111 is connected with described Cycle by Cycle flow-restriction; As shown in Figure 3, Fig. 3 is the internal circuit schematic diagram of Cycle by Cycle flow-restriction 110.It is made up of resistance 1101 and comparator 1102.Wherein, one end connection control chip CS of resistance 1101 introduces pin, for inputting outside former limit peak current detection signal CS, namely detect output with the former limit winding current of described transformer to be connected, resistance 1101 inputs outside former limit peak current detection signal, the other end connects the in-phase input end of comparator 1102, connect the output of current limit threshold dither unit 111 simultaneously, and the output signal Ij of input current limit threshold dither unit 111, the inverting input of comparator 1102 connects internal reference voltage Vref, the output of comparator 1102 is connected with described rest-set flip-flop, its output out is for controlling the shutoff of each turn-on cycle, when former limit peak current reaches the reference voltage V ref of internal reference threshold value, the output out of comparator 1102 reverses, driver output is closed.
As shown in Figure 4, Fig. 4 is the internal circuit of current limit threshold dither unit 111, and it is made up of oscillator, frequency divider and some groups of (n group) current sources and switch.If cycle oscillator is t, then in a large period T0=2n × t, the electric current of Ij will-2
ni0 is to 2
nchange between × I0, the step-length of change is I0, and each step duration is t, and in whole large period T0, the average current of Ij equals zero like this.If n is enough large, I0 is enough little, then Ij can close to a continuous print string ripple; So, described current limit threshold dither unit produces the current signal Ij of one-period change.
Further, as shown in Figure 5, Fig. 5 is that threshold values trembles frequently control system when working in constant current mode, trembles principle schematic frequently.Output signal Ij due to current limit threshold dither unit 111 is the current signal of one-period fluctuation, and its waveform is close to sinusoidal wave.Like this, the current signal Ij of cyclic fluctuation produces the voltage signal Vj of one-period change by resistance Rj, and be superimposed upon on the former limit peak current detection signal CS of transformer, CS1=CS+Ij*Rj=Vref, then CS=Vref-Ij*Rj, namely the amplitude of former limit peak current detection signal CS also can cyclic variation, and then make secondary ON time Tons cyclic variation, due to T=K*Tons, therefore threshold values trembles the operating frequency also generating period change of control system frequently, namely realizes trembling function frequently.Shake due to frequency is periodic, shake in the segment limit Δ F that average frequency Favg is narrower up and down, average operating frequency Favg can not change with frequency jitter, the mean value of former limit peak current detection signal CS also can not change because trembling frequently, therefore average output current Io=0.5 × Ips × Tons/T=Ipp × (NS/NP) × (1/K) is a definite value, therefore namely achieve and tremble function frequently, in turn ensure that the constant of output current.
Embodiment 2
The threshold values present embodiments providing a kind of former limit feedback AC-DC Switching Power Supply trembles control method frequently, and the method and threshold values in embodiment 1 are trembled frequency and controlled corresponding, and wherein, the method can be realized by following steps:
First, the first step, arranges a current limit threshold dither unit be connected with Cycle by Cycle flow-restriction, such as, tremble in frequency control system at the threshold values of Switching Power Supply, the current limit threshold dither unit be connected is set in control chip inside, as shown in Figure 2 with Cycle by Cycle flow-restriction.
Wherein, Cycle by Cycle flow-restriction arranges a resistance and a comparator, and such as, as shown in Figure 3, Cycle by Cycle flow-restriction is made up of resistance 1101 and comparator 1102.Wherein, one end of resistance 1101 connects outside former limit peak current detection signal CS, namely detect pin with the former limit winding current of external transformer to be connected, resistance 1101 inputs outside former limit peak current detection signal CS, resistance 1101 other end connects the in-phase input end of comparator 1102, connect the output of current limit threshold dither unit simultaneously, and the output signal Ij of input current limit threshold dither unit, the inverting input of comparator 1102 connects internal reference voltage Vref, the output of comparator 1102 is connected with described rest-set flip-flop, its output out is for controlling the shutoff of each turn-on cycle, when former limit peak current reaches the reference voltage V ref of internal reference threshold value, the output out of comparator 1102 reverses, driver output is closed.
Then, second step, produces the current signal of one-period change, such as by the described current limit threshold dither unit arranged, as shown in Figure 4, current limit threshold dither unit it be made up of oscillator, frequency divider and some groups of (n group) current sources and switch.If cycle oscillator is t, then in a large period T0=2n × t, the electric current of Ij will-2
ni0 is to 2
nchange between × I0, the step-length of change is I0, and each step duration is t, and in whole large period T0, the average current of Ij equals zero like this.If n is enough large, I0 is enough little, then Ij can close to a continuous print string ripple; So, described current limit threshold dither unit produces the current signal Ij of one-period change.
After forming cyclic variation current signal Ij, perform the 3rd step, the resistance that described current signal Ij is arranged through described Cycle by Cycle flow-restriction, produce a periodically variable voltage signal; Such as, as shown in Figure 5, the output signal Ij due to current limit threshold dither unit is the current signal of one-period fluctuation, and its waveform is close to sinusoidal wave.Like this, the current signal Ij of cyclic fluctuation produces the voltage signal Vj of one-period change by resistance Rj.
Finally, the 4th step, is superimposed on the current sense signal of former limit winding current detecting pin by described periodically variable voltage signal; Such as, as shown in Figure 5, to be superimposed upon on the former limit peak current detection signal CS of transformer described in periodically variable voltage signal Vj, CS1=CS+Ij*Rj=Vref, then CS=Vref-Ij*Rj, namely the amplitude of former limit peak current detection signal CS also can cyclic variation, and then make secondary ON time Tons cyclic variation, due to T=K*Tons, the therefore operating frequency of system also generating period change, namely realizes trembling function frequently.Shake due to frequency is periodic, shake in the segment limit Δ F that average frequency Favg is narrower up and down, average operating frequency Favg can not change with frequency jitter, the mean value of former limit peak current detection signal CS also can not change because trembling frequently, therefore average output current Io=0.5 × Ips × Tons/T=Ipp × (NS/NP) × (1/K) is a definite value, therefore namely achieve and tremble function frequently, in turn ensure that the constant of output current.
So, when being in constant current mode, its operating frequency, in the shake of certain scope periodically, to disperse electromagnetic interference EMI energy, thus significantly reduces EMI.In addition, shake due to frequency is periodic, and shake in the segment limit that average frequency is narrower up and down, therefore the average operating frequency of system remains fixing, thus the average output current of the system of guarantee is constant, namely threshold values trembles the constant-current characteristics of control system frequently not by the impact of frequency jitter.
Should be understood that, for those of ordinary skills, can be improved according to the above description or convert, and all these improve and convert the protection range that all should belong to claims of the present invention.
Claims (2)
1. the threshold values of a former limit feedback AC-DC Switching Power Supply trembles control system frequently, comprise control chip, transformer, NMOS tube, described control chip comprise secondary ON time detecting unit, constant current frequency control unit, output voltage detecting unit, constant voltage frequency control unit, built-in power subsystem, with gate logic, rest-set flip-flop, PFM unit, driver element and Cycle by Cycle flow-restriction, it is characterized in that:
Described control chip also comprises a current limit threshold dither unit, and described current limit threshold dither unit is connected with described Cycle by Cycle flow-restriction;
Described current limit threshold dither unit arranges oscillator, frequency divider and some groups of current sources and switch, for generation of the current signal Ij of one-period fluctuation, and exports described Cycle by Cycle flow-restriction to;
Described Cycle by Cycle flow-restriction arranges resistance Rj and comparator; One end of described resistance Rj is detected pin with the former limit winding current of described transformer and is connected, and the other end connects the in-phase input end of described comparator, and is connected with the output of described current limit threshold dither unit simultaneously;
The inverting input of described comparator connects internal reference voltage Vref, and the output of described comparator is connected with described rest-set flip-flop;
In a large period T0=2n × t, t is cycle oscillator, and n is the group number of current source and switch, and current signal Ij is-2
n× I0 is to 2
nchange between × I0, I0 is the step-length of change, and in whole large period T0, the average current of Ij equals zero, when n is enough large, and enough hour of I0, described current limit threshold dither unit produces the current signal Ij of one-period fluctuation, the current signal Ij of cyclic fluctuation produces the voltage signal Vj of one-period change by resistance Rj, and be superimposed upon on the former limit peak current detection signal CS of transformer, CS=Vref-Ij × Rj, the amplitude also cyclic fluctuation of former limit peak current detection signal CS, make secondary ON time Tons cyclic variation, therefore threshold values trembles the operating frequency also generating period change of control system frequently, shake due to frequency is periodic, shake in the band frequency range delta F that average operating frequency Favg is narrower up and down, therefore average operating frequency Favg can not change with frequency jitter, the mean value of former limit peak current detection signal CS also can not change because trembling frequently, thus average output current is constant.
2. the threshold values of former limit feedback AC-DC Switching Power Supply trembles a control method frequently, it is characterized in that, comprises the steps;
A: a current limit threshold dither unit be connected with Cycle by Cycle flow-restriction is set;
B: the current signal Ij being produced one-period change by described current limit threshold dither unit, in a large period T0=2n × t, t is cycle oscillator, and n is the group number of current source and switch, and current signal Ij is-2
n× I0 is to 2
nchange between × I0, I0 is the step-length of change, and in whole large period T0, the average current of Ij equals zero, when n is enough large, and enough hour of I0, described current limit threshold dither unit produces the current signal Ij of one-period fluctuation;
C: the current signal Ij of the described cyclic fluctuation resistance Rj arranged through described Cycle by Cycle flow-restriction, produces a periodically variable voltage signal Vj;
D: described periodically variable voltage signal Vj is superimposed upon on the former limit peak current detection signal CS of transformer, CS=Vref-Ij × Rj, the amplitude also cyclic fluctuation of former limit peak current detection signal CS, make secondary ON time Tons cyclic variation, therefore threshold values trembles the operating frequency also generating period change of control system frequently, shake due to frequency is periodic, shake in the band frequency range delta F that average operating frequency Favg is narrower up and down, therefore average operating frequency Favg can not change with frequency jitter, the mean value of former limit peak current detection signal CS also can not change because trembling frequently, thus average output current is constant.
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| CN104582101A (en) * | 2013-10-18 | 2015-04-29 | 凹凸电子（武汉）有限公司 | Light source drive circuit as well as controller and method for controlling electric energy supplied to light source |
| TWI514737B (en) | 2013-07-23 | 2015-12-21 | Leadtrend Tech Corp | Controller for generating jitters in a quasi resonant mode and method for generating jitters in a quasi resonant mode |
| CN104348352A (en) * | 2013-07-31 | 2015-02-11 | 通嘉科技股份有限公司 | Controller and method for producing jitter at quasi-resonance mode |
| CN104270009B (en) * | 2014-09-23 | 2017-12-12 | 广东美的制冷设备有限公司 | The power circuit and air conditioner of multi output |
| CN104333216B (en) * | 2014-11-28 | 2017-04-12 | 矽力杰半导体技术(杭州)有限公司 | Switching power supply controller and control method thereof |
| CN105226953B (en) * | 2015-09-23 | 2018-02-02 | 成都芯源***有限公司 | Jitter frequency control circuit and control method thereof |
| CN108513400B (en) * | 2018-04-04 | 2019-11-19 | 泉芯电子技术(深圳)有限公司 | The detection method of inductive current average detection system and its inductive current average detection system |
| CN110380628B (en) * | 2019-05-30 | 2021-02-26 | 深圳市稳先微电子有限公司 | Power conversion control chip and power adapter |
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